- In a large pot of boiling water, cook noodles according to package directions until just tender. 
- Drain and transfer to 12 cup casserole dish. 
- Meanwhile, in a large skillet, heat 2 tbsp of olive oil over medium-high heat. 
- Saute mushrooms for 5 to 7 minutes or until tender. 
- Spread over noodles, along with shrimp, scallops, fish medley and clams. 
- In a small sauce pan, melt remaining butter over medium heat. Whisk in flour, salt and pepper. Cook, stirring constantly for about 2 minutes or until smooth. 
- Gradually whisk in milk and cook, stirring constantly, until thickened. Pour over noodle mixture and sprinkle with cheese. 
- Cover and bake in preheated (350F) oven for 40 to 45 minutes or until hot and bubbly. 
- Remove from oven and preheat broiler. Uncover casserole, sprinkle with paprika and broil for 3 to 5 minutes or until top is golden brown.